<template>
    <div class="progress-bar" @click="onClick">
        <div class="bar-inner">
            <div class="progress" ref="progressRef" :style="progressStyle"></div>
            <div class="progress-btn-wrapper"
             :style="btnStyle"
             @touchstart.prevent="onTouchStart"
             @touchmove.prevent="onTouchMove"
             @touchend.prevent="onTouchEnd">
                <div class="progress-btn"></div>
            </div>
        </div>
    </div>
</template>

<script>
    const progressBtnWidth = 16
    export default {
        name: 'progress-bar',
        emits: ['progress-changing', 'progress-changed'],
        props: {
            progress: {
                type: Number,
                default: 0
            }
        },
        data() {
            return {
                offset: 0
            }
        },
        computed: {
            progressStyle() {
                return `width: ${this.offset}px`
            },
            btnStyle() {
                return `transform:translate3d(${this.offset}px,0,0)`
            }
        },
        watch: {
            progress(newProgress) {
                const barWidth = this.$el.clientWidth - progressBtnWidth
                this.offset = barWidth * newProgress
            }
        },
        created() {
            this.touch = {}
        },
        methods: {
            onTouchStart(e) {
                this.touch.x1 = e.touches[0].pageX
                this.touch.beginWidth = this.$refs.progressRef.clientWidth
            },
            onTouchMove(e) {
                const delta = e.touches[0].pageX - this.touch.x1
                const tempWidth = this.touch.beginWidth + delta
                const barWidth = this.$el.clientWidth - progressBtnWidth
                const progress = Math.min(1, Math.max(tempWidth / barWidth, 0))
                this.offset = barWidth * progress
                this.$emit('progress-changing', progress)
            },
            onTouchEnd() {
                const barWidth = this.$el.clientWidth - progressBtnWidth
                const progress = this.$refs.progressRef.clientWidth / barWidth
                this.$emit('progress-changed', progress)
            },
            onClick(e) {
                const rect = this.$el.getBoundingClientRect()
                const offsetWidth = e.pageX - rect.left
                const barWidth = this.$el.clientWidth - progressBtnWidth
                const progress = offsetWidth / barWidth
                this.$emit('progress-changed', progress)
            }
        }
    }
</script>

<style lang="scss" scoped>
  .progress-bar {
    height: 30px;
    .bar-inner {
      position: relative;
      top: 13px;
      height: 4px;
      background: rgba(0, 0, 0, 0.3);
      .progress {
        position: absolute;
        height: 100%;
        background: $color-theme;
      }
      .progress-btn-wrapper {
        position: absolute;
        left: -8px;
        top: -13px;
        width: 30px;
        height: 30px;
        .progress-btn {
          position: relative;
          top: 7px;
          left: 7px;
          box-sizing: border-box;
          width: 16px;
          height: 16px;
          border: 3px solid $color-text;
          border-radius: 50%;
          background: $color-theme;
        }
      }
    }
  }
</style>